1. Field of the Invention
The present invention relates to semiconductor wafer processing systems and, more particularly, to a high temperature chemical vapor deposition (CVD) chamber with a heated inside liner, and a temperature-controlled outer chamber body.
2. Description of the Background Art
Titanium nitride (TiN) film has found wide applications in ultra large-scale integrated circuits (ULSI) as a diffusion barrier and as an adhesion layer for tungsten contacts. Low temperature reactive sputtering of Ti in the presence of nitrogen has been used in the past to deposit TiN films upon semiconductor wafers. However, as device geometries become increasingly smaller, the resulting step coverage from a sputtered TiN film is no longer adequate. Therefore, chemical vapor deposition (CVD) techniques have become the methods of choice in ULSI applications. For example, TiN film from a titanium tetrachloride based CVD process can be used as a high aspect ratio contact barrier, a capacitor top electrode or in plug fill processes below 0.18 xcexcm.
Both cold wall and hot wall low pressure chemical vapor deposition (LPCVD) processes have been used for depositing TiN films using a reaction between titanium tetrachloride (TiCl4) and ammonia (NH3). A cold wall reactor contains a wafer that is heated to a temperature above the reaction temperature of the process gases, e.g., over 650xc2x0 C., by a halogen lamp that is located external to the chamber. However, since the chamber walls are cold (unheated), process by-products such as adduct ammonia salts will detrimentally form on the interior surfaces of the cold chamber walls or other cold surfaces. During thermal cycling of the chamber, these deposits may flake and fall on a wafer causing contamination and reducing wafer yield. Since these reaction by-products cannot be removed by in-situ chamber cleaning processes, frequent chamber disassembly and cleaning is required. This necessitates the opening of the chamber to the atmosphere, and results in considerable down time for the chamber.
Alternatively, quartz hot wall reactors have been used to form high quality TiN films. The heated walls of these reactors help reduce accumulation of undesirable deposits, such as adduct ammonia salts, on the interior chamber walls. However, hot wall chambers can be dangerous to operate because of the high temperature of the walls, e.g., 150-200xc2x0 C. Furthermore, it is difficult to achieve uniform heating of the chamber walls and other interior surfaces such that no undesirable deposits form.
One possible solution is the use of a chamber liner, such as that disclosed in U.S. Pat. No. 5,348,587, issued on Sep. 20, 1994, to Eichman et al., entitled xe2x80x9cApparatus for Elimination of Low Temperature Ammonia Salts in TiCl4 NH3 CVD Reaction,xe2x80x9d which is a continuation of U.S. Pat. No. 5,271,963, issued on Dec. 21, 1993. Both patents are herein incorporated by reference. Eichman et al. discloses an inside liner which is partly heated by lamps external to the chamber, and partly heated by a secondary plasma. This heated liner is located within a cold reactor wall enclosure. The heated liner lies against the inner surface of the cold reactor wall, and, as such, is only partially insulated from the reactor wall. Not only does this contact promote excessive thermal conduction to the reactor wall resulting in the chamber wall becoming dangerously hot, but additional heating of the liner will be needed to compensate for the heat lost to the wall.
Therefore, a need exists in the art for a CVD chamber having a heated liner which substantially defines a chamber cavity and is thermally isolated from the external chamber body.
The disadvantages of the prior art are overcome by an apparatus for processing a wafer having a chamber body that encloses a chamber liner, where the liner is maintains a spaced apart distance from the chamber body such that the liner is maintained at a higher temperature than the chamber body. As such, the liner can be maintained at a temperature that reduces the amount of deposition on the liner while maintaining a safe temperature for the chamber body.
More specifically, the present invention relates to a process chamber system for high temperature film deposition, e.g., using a reaction between titanium tetrachloride (TiCl4) and ammonia (NH3) to deposit titanium nitride (TiN). The system comprises a process chamber and an exhaust assembly. The process chamber has an inside liner which is maintained at a temperature of approximately 150-250xc2x0 C., while the chamber body is maintained at a temperature of approximately 60-65xc2x0 C. or below. The liner can either be heated directly by a resistive heater embedded in the liner, or indirectly by a heated wafer support pedestal. The liner, which is substantially cylindrical, is enclosed within the bucket-shaped chamber body having a cylindrical wall and a base. Isolating pins are located between the bottom of the liner and the inside surface of the chamber base such that a spacing is maintained between the liner and the chamber body, i.e., the liner only contacts the chamber body through the isolating pins. Excellent thermal isolation is achieved between the liner and the chamber body because of the low thermal conductivity resulting from the small contact area between the isolating pins and the liner.
The process chamber further comprises a heated wafer support pedestal for supporting and heating a semiconductor wafer and a showerhead for separately introducing TiCl4 and NH3 into the process chamber into a space above the wafer. The wafer is maintained at a temperature of approximately 600-700xc2x0 C. such that a thermal reaction occurs at the surface of the wafer between TiCl4 and NH3, resulting in the formation of a TiN film upon the wafer.
The exhaust assembly is connected to the process chamber to allow for continuous pumping of gases away from the process chamber. In one embodiment, a substantial portion of the exhaust assembly is maintained at approximately 150xc2x0 C-200xc2x0 C. by the use of several heaters disposed on the outside walls of the exhaust assembly. Such heating reduces reaction by-product accumulation within the exhaust assembly.